Previously, considerable difficulty had been experienced in providing internally pressurizable multi-layered envelopes wherein the envelope was a flat or uniformly contoured supporting surface, with the capacity of being pressurized to relatively high levels. Previously much of the absorbed, redistributed, and stored impact/shock energy was lost and not returned in a useful form because of the requirement to encapsulate the unit in a viscoelastic foam acting as a moderator to develop the desired smooth or contoured surface.
It was simply not possible to provide a product wherein much (greater than 60%) of the load supporting material of the product was a gas under pressure. With the former product, less than 40% of the energy of impact on the structure was returned in a beneficial, efficient and comfortable manner, the balance of the energy being absorbed and dissipated as heat. The present design is capable of returning, in a useful form, up to 92% of the otherwise wasted energy. In addition, superior cushioning and compliance are also provided, which significantly reduces damaging impact shock loads to the foot and legs to levels under 12 G's.
The new product was developed because difficulty had been experienced with the prior products in producing light weight, long-life, high-pressure inflated structures for use in foot wear and the like which possessed a high degree of resilience and compliance wherein the shock energy absorbed, redistributed and stored at impact is efficiently returned as useful energy in a smooth manner, at a rate equal to or greater than the rate at which the applied load is removed from the devices. Success of this new product depended upon solving several basic problems: 1) separation (delamination) between the tensile element (fabric layer with drop threads) and the gas containing barrier layer, when subjected to high loads with long-term cyclical fatigue conditions, 2) crushing, abrasion, and bending fatigue failure of the drop-threads, 3) hydrolytic degradation failure of the drop threads, 4) fungus, bacteria and hydrolytic stress fracture of the barrier material, 5) unravelling of the tensile-elements immediately adjacent to the cut edges of the cloth, when subject to high loads and bending and flexing, 6) puncture and abrasion failure of the barrier film, 7) leakage of the pressurizing gas at the perimeter seal, caused by fiber filaments extending from the sides of the tensile cloth being trapped in, and bridging the perimeter barrier seal so as to create minute leakage paths through which pressurizing gas could slowly leak out.
In addition to the above problems, one of the more difficult challenges was the provision of a sealed, permanently inflated cushioning device with flat surfaces, as contrasted to tubular or rounded chambers, and which could be made relatively thin so as to achieve 100% air support and cushioning and which possessed sufficient fatigue resistance to withstand millions of compression cycles in use. In the case of consumer items, especially footwear, a useful life of several years is essential. Furthermore this product must maintain the unique and beneficial cushioning properties, without significant degradation throughout its full lifetime. As is apparent, a significant loss or gain of pressure over a period of time is not acceptable, especially in consumer products. It is also desirable to provide an inflated product capable of withstanding relatively high localized loads without bottoming out, such as the loads typically encountered in athletic activities.
For example, in running or other sport events which involve running or jumping, there are substantial localized loads during heel strike or push off. If the cushioning device bottoms out, then the entire purpose of the cushion is compromised. For most conditions encountered, to prevent bottoming out, the inflated product either may be made sufficiently thick or highly pressurized or both. Another desirable approach is to use smaller chambers inflated at lower pressures, and positioned under the load bearing surface so that there is little or no accumulator volume into which the gas may escape. Relatively high pressurization of the prior art inflated devices with rounded tubular chambers produced an uncomfortable feel, unless encapsulated with foam, or used with some other type of surface/contour moderator element.
The load/deflection curve of this tensile product achieves totally new, unique and beneficial cushioning characteristics never before possible with other prior art load cushioning devices.
The load deflection characteristics of my earlier inventions, U.S. Pat. No. 4,183,156, provided a very soft cushioned support under light loads. Then, with progressively heavier loads, the supportive force increased either in a linear or in an exponential manner. This type of load/deflection characteristic is suitable for many applications. However, there are other uses where it is very desirable that the pressurized pneumatic cushioning device initially exhibit a very firm cushion support under light to moderate compression loads, a degree of support greater than the product of the area of the applied load times the internal working pressure. Then, when greater compression loads are applied, the device automatically, at a predetermined load, changes from the firm, board-like cushioning support and exhibits a soft, relatively consistent and gradual increasing level of cushioned support throughout the full, available displacement of the inflated device.
This type of cushioned support embraces substantially different, new novel technology from the prior art. New, novel and highly useful products are now possible that were impossible using the prior art.
Thus, a need exists for an improved essentially permanently pre-pressurized product which has advantages over the prior art inflated products. It is also apparent that there are the practical considerations of being able to manufacture such products relatively inexpensively, at relatively high volume and of a very high quality which assures that the product will be free of leaks and have an acceptable service life even when built as a permanent and integral part of the footwear. It is also an advantage to be able to provide a gas pressurized load bearing cushioning member which may be formed in various shapes,thicknesses, and contours.